Polishing composition

ABSTRACT

Proposed is a polishing composition including hydroxyethyl cellulose, water and abrasive grains, wherein the hydroxyethyl cellulose has a molecular weight of 500,000 or more and 1,500,000 or less, and the mass ratio of the hydroxyethyl cellulose to the abrasive grains is 0.0075 or more and 0.025 or less.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2014-73436, the content of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a polishing composition.

BACKGROUND ART

Recently, the miniaturization of semiconductor devices has progressedwith the high integration or the like of integrated circuits, andconsequently, in addition to high flatness, a high level reduction ofsurface defects has been required for semiconductor substrates(hereinafter, also simply referred to as substrates) such assemiconductor wafers (hereinafter, also simply referred to as wafers).

For the purpose of reducing such surface defects, polishing of thesurface of substrates with a polishing composition including awater-soluble polymer, which is a component enhancing the wettability tosemiconductor substrates, has been considered.

Such a polishing composition is described in, for example, PatentLiterature 1. Patent Literature 1 describes a polishing compositionincluding hydroxyethyl cellulose as a water-soluble polymer.

Surface defects having various sizes are present in a mixed manner onthe surface of a substrate before polishing; however, with such aconventional polishing composition as described in Patent Literature 1,it is impossible to selectively remove surface defects having specificsizes. Accordingly, for example, in the case where a large number ofsurface defects having specific sizes are present on the substratesurface, or in the case where polishing is performed for the purpose ofremoving surface defects having specific sizes among the surface defectspresent in a mixed manner, there is a problem that it is impossible tosufficiently remove the surface defects having the targeted sizes withthe polishing composition described in Patent Literature 1.

CITATION LIST Patent Literature

-   Patent Literature 1: Japanese Patent Laid-Open No. 2010-34509

SUMMARY OF THE INVENTION Technical Problem

Accordingly, in view of such conventional problems as described above,an object of the present invention is to provide a polishing compositioncapable of selectively reducing the surface defects having specificsizes present on the surface of a polishing object such as asemiconductor substrate.

Solution to Problem

The polishing composition according to the present invention includeshydroxyethyl cellulose, water and abrasive grains, wherein thehydroxyethyl cellulose has a molecular weight of 500,000 or more and1,500,000 or less, and the mass ratio of the hydroxyethyl cellulose tothe abrasive grains is 0.0075 or more and 0.025 or less.

In the present invention, the abrasive grains may be contained in anamount of 5% by mass or more and 20% by mass or less.

In the present invention, the polishing composition may further includeammonia.

In this case, the ammonia may be contained in an amount of 0.1% by massor more and 1.0% by mass or less.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the proportions of surface defects afterpolishing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, the polishing composition according to the presentinvention is described.

The polishing composition of the present embodiment includeshydroxyethyl cellulose, water and abrasive grains, wherein the molecularweight of the hydroxyethyl cellulose is 500,000 or more and 1,500,000 orless, and the mass ratio of the hydroxyethyl cellulose to the abrasivegrains is 0.0075 or more and 0.025 or less.

As the hydroxyethyl cellulose in the present embodiment, hydroxyethylcellulose having a molecular weight of 500,000 or more and 1,500,000 orless, preferably 800,000 or more and 1,200,000 or less is used.

The molecular weight falling within the above-described range allows thepolishing composition to exert removability particularly excellent forthe surface defects having specific sizes in a polishing object.

Hydroxyethyl cellulose can improve the wettability; in particular, thehydroxyethyl cellulose having the molecular weight falling within theabove-described range improves the wettability to a polishing object,and can reduce the particles and the like on the surface of thepolishing object after polishing.

The molecular weight of hydroxyethyl cellulose in the present embodimentmeans the weight average molecular weight measured by using the GFC (GelFiltration Chromatography) method, and specifically means the valuemeasured by the measurement method shown in below-described Examples.

The polishing composition of the present embodiment includes water. Thehydroxyethyl cellulose is a hydrophilic polymer, hence easily yields anaqueous solution when mixed with water, and thus, as described above,can exert functions such as improvement in the removability of thesurface defects having specific sizes in a polishing object and thewettability.

The content of water is not particularly limited; water can beappropriately mixed.

When the polishing composition is used as diluted at the time of use,the polishing composition is prepared as a high-concentration liquidhaving a higher concentration than the concentration desired at the timeof use, and water may be mixed as a diluting liquid at the time ofdilution.

The polishing composition of the present embodiment includes abrasivegrains.

Examples of the abrasive grains include: grains made of metal oxidessuch as silica, alumina, ceria and titania; silicon nitride grain;silicon carbide grain; and boron nitride grain. Preferable among theseis silica; particularly preferable among these is colloidal silica suchas spherical or non-spherical colloidal silica.

When the abrasive grains are colloidal silica, a hydroxyethyl celluloseaqueous solution is easily adsorbed to the abrasive grains and theremovability of the surface defects having specific sizes can be moreenhanced, as described below, and thus it is preferable.

Of the colloidal silicas, non-spherical colloidal silica is preferable.Non-spherical colloidal silica allows the hydroxyethyl cellulose aqueoussolution to be more easily adsorbed thereto through the concomitantpresence with hydroxyethyl cellulose in the polishing composition andallows the removability of the surface defects having specific sizes tobe more enhanced, as described below, and thus it is preferable.

In the polishing composition of the present embodiment, the ratio of thecontent (% by mass) of the hydroxyethyl cellulose to the content (% bymass) of the abrasive grains is 0.0075 or more and 0.025 or less andpreferably 0.0075 or more and 0.02 or less.

The ratio of the content (% by mass) of the hydroxyethyl cellulose tothe content (% by mass) of the abrasive grains in the polishingcomposition falling within the above-described range allows theremovability of the surface defects having specific sizes to be moreenhanced. At the same time, such a ratio as described above allows thewettability of the surface of a polishing object after polishing to beimproved.

The content of the abrasive grains in the polishing composition of thepresent embodiment is not particularly limited, but is, for example, 5%by mass or more and 20% by mass or less.

The content of the abrasive grains falling within the above-describedrange is preferable, because such a content allows the polishing speedto be regulated appropriately.

The grain size of the abrasive grains is not particularly limited, butexamples of the grain size include an average grain size of 50 nm ormore. The average grain size of the abrasive grains falling within theabove-described range is preferable because the surface defects havingspecific sizes present on the surface of a polishing object can be moreselectively reduced.

The average grain size of the present embodiment is measured by usingthe DLS (dynamic light scattering) method. More specifically, theaverage grain size of the present embodiment means the average grainsize in the polishing composition, as measured by using an apparatusdescribed in below-described Examples. In other words, when the abrasivegrains form clusters in the polishing composition as described below,the average grain size means the average grain size of the clusters.

The polishing composition of the present embodiment includes thehydroxyethyl cellulose, water and the abrasive grains, and consequentlythe following interactions are considered to occur.

Specifically, in the polishing composition, part of the hydroxyethylcellulose is adsorbed to the surface of the abrasive grains such ascolloidal silica. Accordingly, in the polishing composition, there arethe hydroxyethyl cellulose in a state of being adsorbed to the abrasivegrains, and the hydroxyethyl cellulose not adsorbed to the abrasivegrains and mixed in the polishing composition. It is considered thatwhen the hydroxyethyl cellulose is adsorbed to the abrasive grains, theabrasive grains form clusters through the action of the hydroxyethylcellulose. The larger the molecular weight of the hydroxyethyl celluloseor the larger the content of the hydroxyethyl cellulose in the polishingcomposition, the larger the clusters tend to be.

It is considered that depending on the size and the amount of theclusters, performance of reducing the surface defects having specificsizes present on the surface of a polishing object is varied.

The hydroxyethyl cellulose not adsorbed to the abrasive grains and mixedin the polishing composition can improve the wettability to a polishingobject.

Accordingly, it is considered that by establishing a balance between thehydroxyethyl cellulose adsorbed to the abrasive grains and thehydroxyethyl cellulose not adsorbed to the abrasive grains, thepolishing composition of the present embodiment can reduce the surfacedefects having specific sizes present on the surface of a polishingobject.

In the polishing composition of the present embodiment, the proportionof the hydroxyethyl cellulose adsorbed to the abrasive grains ispreferably 30% by mass or more and 99% by mass of the total amount ofthe hydroxyethyl cellulose in the polishing composition.

When hydroxyethyl cellulose having a molecular weight of 800,000 to1,000,000 is used as the hydroxyethyl cellulose, the proportion of thehydroxyethyl cellulose adsorbed to the abrasive grains is 60% by mass ormore and 99% by mass or less, and preferably 70% by mass or more and 99%by mass or less of the total amount of the hydroxyethyl cellulose in thepolishing composition.

When hydroxyethyl cellulose having a molecular weight of 500,000 to800,000 is used as the hydroxyethyl cellulose, the proportion of thehydroxyethyl cellulose adsorbed to the abrasive grains is 30% by mass ormore and 99% by mass or less of the total amount of the hydroxyethylcellulose in the polishing composition.

In the present embodiment, the grain size of the abrasive grains(clusters) and the proportion of the hydroxyethyl cellulose adsorbed tothe abrasive grains mean the grain size and the proportion at the timeof use of the polishing composition, respectively.

The polishing composition of the present embodiment may further includeammonia.

The inclusion of ammonia allows the surface defects having specificsizes present on the surface of a polishing object to be reduced moresufficiently, and thus it is preferable.

The content of ammonia is not particularly limited, but, examples of thecontent of ammonia include 0.1% by mass or more and 1.0% by mass orless, and preferably 0.25% by mass or more and 0.75% by mass or less.

The content of ammonia falling within the above-described range allowsthe surface defects having specific sizes present on the surface of apolishing object to be more sufficiently reduced, and thus it ispreferable.

The content of ammonia falling within the above-described range alsoallows the pH of the polishing composition to be regulated so as to fallwithin an appropriate range, and thus it is preferable.

The polishing composition of the present embodiment may further includeother components.

Examples of the other components include: a pH adjuster, a surfactantand a chelating agent.

The polishing composition of the present embodiment may be prepared as ahigh concentration liquid having a higher concentration than the desiredconcentration at the time of use, and may be diluted at the time of use.

When the polishing composition is prepared as such a high concentrationliquid, the high concentration liquid is convenient for storage andtransportation.

When the polishing composition is prepared as a high concentrationliquid, examples of the preparation include a preparation in which thehigh concentration liquid is prepared so as to have a concentrationcapable of being diluted at the time of use by a factor ofapproximately, for example, 5 to 100-fold, preferably 20 to 60-fold andmore preferably 21 to 41-fold.

The polishing composition of the present embodiment is used for thepolishing of polishing objects required to have a high flatness and ahigh-level reduction in the surface defects as in semiconductorsubstrates such as semiconductor wafers. In these polishing objects,fine surface defects are also required to be sufficiently removed.

For example, on the surface of the wafers, there are surface defectshaving various sizes and various shapes. Specifically, for example,minute surface defects having heights of less than 10 nm and surfacedefects relatively larger in size, having heights of 10 nm or more, arepresent in a mixed manner. Moreover, among the minute surface defectshaving heights of less than 10 nm, there are relatively larger surfacedefects having heights of 3 nm or more and particularly minute surfacedefects having heights of less than 3 nm. In order to reduce suchsurface defects having various sizes, the polishing is performed aplurality of times. For example, it is considered that by the firstpolishing, the surface defects having larger sizes are made smaller, andby the final polishing, minute surface defects are removed.

The height and the width of a surface defect as referred to in thepresent embodiment means the height and the width as measured with anatomic force microscope (AFM).

The determination of the presence or absence of the surface defects isperformed by using the count of the number of the surface defects.Accordingly, when there are countable surface defects regardless of thesizes of the defects, the number of counts is large and it is determinedthat the surface defects are not reduced. However, in theabove-described plurality of times of polishing, when the surfacedefects having large sizes remain in the final polishing stage even in asmall number, the surface defects cannot be sufficiently reduced in thefinal polishing designed for the purpose of removing minute surfacedefects. Accordingly, it is important to remove, before the finalpolishing, the surface defects having sizes hardly removable in thefinal polishing, instead of reducing the number of counts of the surfacedefects.

The polishing composition of the present embodiment can remove thesurface defects having specific sizes. Examples of the surface defectshaving the sizes removable in the largest number with the polishingcomposition of the present embodiment include relatively larger surfacedefects having heights of 3 nm or more and less than 10 nm. In otherwords, the polishing composition of the present embodiment leaves therelatively smaller minute surface defects having heights of less than 3nm, and can efficiently remove the surface defects having relativelylarger sizes of 3 nm or more in height.

The polishing composition of the present embodiment can remove thesurface defects having such specific sizes, and consequently has thefollowing merits. Specifically, in such a case of performing a pluralityof times of polishing as described above, by using the polishingcomposition of the present embodiment as the polishing compositionbefore the final polishing, the surface defects of a polishing objectafter the final polishing can be sufficiently reduced. Alternatively, byusing the polishing composition of the present embodiment as thepolishing composition for polishing a polishing object having a largenumber of relatively larger surface defects, the surface defects can besufficiently reduced.

The surface of a semiconductor substrate that is a polishing objecthaving been subjected to the treatment with the polishing composition ofthe present embodiment has such a configuration in which the proportionof the number of counts of relatively small surface defects havingheights of less than 3 nm of the surface defects measured by using asurface defect inspection apparatus such as a confocal optical systemlaser microscope (MAGICS M5640, manufactured by Lasertec Corp.) is 45%or more, preferably 70% or more and more preferably 90% or more of thenumber of counts of the whole of the surface defects. In other words,the surface of the semiconductor substrate is in a state in which theremaining proportion of the surface defects other than the relativelysmall surface defects is small.

The polishing composition of the present embodiment is as describedabove, but it should be construed that the embodiment disclosed ispresented in all aspects as exemplification for describing the presentinvention, and the present invention is not limited to the embodiment.The scope of the present invention is defined not by the foregoingdescription but by the appended claims, and is intended to include allthe modifications in the meaning of equivalence to the claims and withinthe scope of the present invention.

The present inventors made a diligent study in order to solve suchproblems as described above, and consequently have achieved the presentinvention by discovering that surface defects having specific sizes canbe selectively reduced by allowing the polishing composition to includehydroxyethyl cellulose having a specific molecular weight and abrasivegrains in a specific ratio.

The polishing composition according to the present invention is apolishing composition including hydroxyethyl cellulose, water andabrasive grains, wherein the molecular weight of the hydroxyethylcellulose is 500,000 or more and 1,500,000 or less, and the mass ratioof the hydroxyethyl cellulose to the abrasive grains is 0.0075 or moreand 0.025 or less.

According to the present invention, the hydroxyethyl cellulose has amolecular weight of 500,000 or more and 1,500,000 or less, and the massratio of the hydroxyethyl cellulose to the abrasive grains is 0.0075 ormore and 0.025 or less, and hence the surface defects having specificsizes present on the surface of a polishing object can be selectivelyreduced.

In the present invention, when the content of the abrasive grains in thepolishing composition falls within such a range as described above, thesurface defects having specific sizes present on the surface of apolishing object can be more selectively reduced.

In the present invention, when the polishing composition furtherincludes ammonia, the surface defects having specific sizes present onthe surface of a polishing object can be more sufficiently reduced.

When the polishing composition includes ammonia in such a content rangeas described above, the surface defects having specific sizes present onthe surface of a polishing object can be more selectively reduced.

As described above, according to the present invention, the surfacedefects having specific sizes present on the surface of a polishingobject such as a semiconductor substrate can be selectively reduced.

EXAMPLES

Hereinafter, Examples of the present invention are described; however,the present invention is not limited to these Examples.

(Hydroxyethyl Cellulose)

The hydroxyethyl celluloses shown in Table 1 having different molecularweights (500,000, and 1,000,000) were prepared.

The molecular weights of the hydroxyethyl celluloses are the molecularweights measured by the following method.

(Measurement of Molecular Weight)

The molecular weight is a value of the weight average molecular weightobtained by the following measurement.

The measurement was performed by using a GFC apparatus (Model PU-2085plus system, manufactured by JASCO Corp.) as the measurement. apparatus,two serially connected columns Asahipak GF-71.0HQ and Asahipak GF-310HQmanufactured by Shodex Co., Ltd., and a 0.7% aqueous solution of sodiumchloride as an eluent.

The hydroxyethyl cellulose (HEC), the abrasive grains (silicon dioxideproduced by sol-gel method, grain size in water: 66 nm by dynamic lightscattering), ammonia and the balance water were mixed according to thecompositions shown in Table 1, to yield the polishing compositions ofExamples and Comparative Example.

The polishing compositions were each diluted by a factor of 41-fold withwater, silicon wafers (12 inch) as objects to be polished were polishedwith the diluted polishing compositions under the following polishingconditions, the surface defects after polishing were measured by thefollowing method, and the results thus obtained are shown in Table 1.

(Polishing Conditions)

Polishing apparatus: SPP800S (manufactured by Okamoto Machine ToolWorks, Ltd.)

Polishing pad: POLYPAS 24T (manufactured by Fujibo Ehime Co., Ltd.)

Platen speed: 40 rpm

Polishing load: 120 gf/cm²

Flow rate: 0.6 L/min

Object to be polished: 12-inch Silicon wafer

Polishing time: 300 sec

(Measurement Method of Surface Defects)

The wafers after polishing under the above-described polishingconditions were washed with an ammonia/hydrogen peroxide mixed liquid,and then the measurement (edge exclusion EE: 5 mm, Slice level: D37 mV)of the surface defects was performed by using a measurement apparatus(MAGICS M5640, manufactured by Lasertec Corp.).

On the basis of the coordinates of the defects measured by MAGICS, themeasurement of the defects was performed by using the measurementapparatus AFM SAP465 (manufactured by Seiko Instruments Inc.).

From these two types of measurement results, the surface defects wereclassified into Types A to F by the following method, and theproportions of the respective surface defects are shown in the graph ofFIG. 1. In Table 1, the proportions of the respective types are shown bypercent.

(Classification of MAGIC Review Images)

In the classification method of the MAGICS review images, according tothe order of the white and black portions varying from the left towardthe right of the image in the defective portions of each of the reviewimages, the MAGIC review images were classified into the following TypesA to F. For the analysis of the MAGICS review images, a band pass filterwas used.

On a MAGICS review image, due to the effect of the band pass filter,when the defects are extremely small (low), the color varies three timesas a sequence of white→black→white or as a sequence ofblack→white→black. Which of the sequence of white→black→white and thesequence of black→white→black corresponds to the low height defects isanalyzed with AFM.

Type A: White-black-white, and scratch-like image

Type B: White-black-white

Type C: Black-white-black

Type D: White-black

Type E: Black-white

Type F: Black

(Dimension of Surface Defects)

The respective types of the defects were measured with AFM, and thedimensions of the respective types of defects were found to fall withinthe following ranges.

Specifically, the defects were classified into the following types A toF.

Type A: Height: less than 3 nm, width: 50 to 200 nm, length: 200 or more

Type B: Height: less than 3 nm, width: 150 to 350 nm

Type C: Height: 3 nm or more and less than 10 nm, width: 50 to 70 nm

Type D: Height: 10 nm or more and 30 nm or less, width: 70 to 250 nm

Type E: Height: 10 nm or more and 50 nm or less, width: 100 to 300 nm

Type F: Height: more than 50 nm, width: more than 150 nm

Type A is a scratch⁻like defect having a length component, and Types Bto F are dot-like or irregular defects.

(pH)

The pH of each of the polishing compositions and the pH of each of the41-fold diluted liquids of these polishing compositions at a liquidtemperature of 25° C. were measured with a pH meter (manufactured byHoriba, Ltd.).

(Measurement of Adsorbed Hydroxyethyl Cellulose)

Each of the polishing compositions was diluted by a factor of 41-foldwith water, a 1.5 mg sample was obtained from the diluted polishingcomposition, and the sample was centrifugally separated by using thecentrifuge MCD-2000 (manufactured by As One Corp) at 14,000 rpm for 10min. Subsequently, each of the centrifuged samples was separated intothe precipitate and the supernatant liquid, the supernatant liquid wasremoved, and the TOC (Total Organic Carbon) amount of each of thesupernatant liquids and the TOC of each of the polishing compositionswere measured with the measurement apparatus Siervers 900 (manufacturedby GE Co.). From the measurement results, the proportion of the adsorbedhydroxyethyl cellulose in each of the polishing compositions wascalculated by the following formula 1, and the results thus obtained areshown in Table 1.

Proportion of adsorbed hydroxyethyl cellulose (%)=(TOC of polishingcomposition−TOC of supernatant liquid)/(TOC of polishingcomposition)×100   (Formula 1)

(Measurement of Grain Size of Clusters)

The grain size of the abrasive grains (clusters) in the 41-fold dilutedliquid of each of the polishing compositions was measured.

The grain sizes were measured by using, as the measurement apparatus,the zeta potential/grain size measurement system ELSZ-2 (manufactured byOtsuka Electronics Co., Ltd.). The results thus obtained are shown inTable 1.

TABLE 1 Abrasive grain NH₃ HEC HEC concentration/ Molecular Silicaconcentration NH₃ concentration HEC concentration silica weight ofconcentration (%) concentration (%) concentration (%) concentration HECExample 1 95000 9.5 5000 0.5 1500 0.15 0.0158 1000000 Example 2 950009.5 5000 0.5 750 0.075 0.0079 1000000 Comparative 95000 9.5 5000 0.53000 0.3 0.0316 1000000 Example 1 Example 3 95000 9.5 2500 0.25 15000.15 0.0158 1000000 Example 4 95000 9.5 7500 0.75 1500 0.15 0.01581000000 Example 5 95000 9.5 5000 0.5 750 0.075 0.0079 500000 pH ofProportion Proportion Grain undiluted Proportion of Proportion ofProportion of Proportion of of of Adsorbed size (nm) liquid ×41 pH TypeA Type B Type C Type D Type E Type F Others HEC Example 1 86.4 10.6 9.82.5% 91.0% 2.5% 0.5% 1.0% 1.5% 1.0% 74% Example 2 82.0 10.7 9.8 4.0%80.0% 6.0% 4.0% 3.0% 1.0% 2.0% 72% Comparative 102.1 10.5 9.8 12.0%56.0% 10.0% 8.0% 6.0% 5.0% 3.0% 64% Example 1 Example 3 142.7 10.3 9.66.0% 79.0% 3.0% 7.0% 0.0% 4.0% 1.0% 82% Example 4 84.7 10.8 9.9 2.0%78.1% 5.5% 9.0% 1.0% 4.0% 0.5% 72% Example 5 75.8 10.8 9.8 2.5% 77.6%8.5% 5.5% 1.5% 3.5% 1.0% 39%

As can be seen from Table 1, the proportions of Type B surface defectswere large on the surfaces of the wafers after polishing with thepolishing compositions of Examples. In other words, the surface defectsother than Type B surface defects were sufficiently removed.

1. A polishing composition comprising hydroxyethyl cellulose, water andabrasive grains, wherein the hydroxyethyl cellulose has a molecularweight of 500,000 or more and 1,500,000 or less; and the mass ratio ofthe hydroxyethyl cellulose to the abrasive grains is 0.0075 or more and0.025 or less.
 2. The polishing composition according to claim 1,wherein the abrasive grains are contained in an amount of 5% by mass ormore and 20% by mass or less.
 3. The polishing composition according toclaim 1, further comprising ammonia.
 4. The polishing compositionaccording to claim 3, wherein the ammonia is contained in an amount of0.1% by mass or more and 1.0% by mass or less.
 5. The polishingcomposition according to claim 2, further comprising ammonia.
 6. Thepolishing composition according to claim 5, wherein the ammonia iscontained in an amount of 0.1% by mass or more and 1.0% by mass or less.